SPRINGFIELD -- Jurors in the murder trial of Nickolas Lacrosse heard the trial take a different path Wednesday as a defense witness said Lacrosse is not criminally responsible for the fatal stabbing of Mauke.

Neuropsychologist Thomas Deters, of Cambridge, testified Lacrosse was in a dissociative state on Feb. 11, 2015, when he stabbed his 17-year-old ex-girlfriend 32 times on the kitchen floor of her Prentice Street home.

He said Lacrosse remembers going to Mauke's house and arguing with her that day, but then his next memory is standing on a corner outside her house.

Deters, testifying in the Hampden Superior Court trial, said he spent 18 hours with Lacrosse, seven doing tests and 11 interviewing him. He also reviewed school and health records and talked to Lacrosse's mother and a friend of Lacrosse.

Defense lawyer Alan J. Black had deferred his opening statement until the start of the defense case. On Wednesday morning he told jurors they would hear testimony that Lacrosse is not guilty because a mental defect prevented him from forming the necessary intent under the law to commit the crime.

Up until this point in the trial, Black had been using cross-examination to challenge prosecution evidence that showed Lacrosse, 23, killed Mauke.

One of the first questions Assistant District Attorney Mary Sandstrom asked Deters on cross-examination was whether Lacrosse admitted killing Mauke.

Deters said Lacrosse didn't say those words, but Lacrosse "came to the conclusion he likely did" kill the Sabis High School senior.

"He's an intelligent young man," Deters said of Lacrosse.

According to Deters, an "intensely emotional event" can trigger the dissociative state. On Feb. 11, 2015, the event was an argument with Mauke at her home. Deters said the dissociative state started after the verbal argument and ended after the stabbing when Lacrosse was outside.

Lacrosse had three times over the years had short periods of a dissociative state, Deters said. In one, he slapped another teen on a bus; in another, he charged at a man he didn't know when he thought the man was hurting a woman; and in the other one, he became enraged when a relative parked on his family home's lawn.

In each case, Lacrosse remembered what led up to the violence or confrontation, and what came after, but not the acts, Deters said.

He said Lacrosse has a history of depression and other mental health disorders and used alcohol and marijuana excessively. Lacrosse was not under the influence of anything on Feb. 11, 2015, Deters said.

Deters testified Lacrosse said he went to Mauke's house for closure, because he thought she had ended the relationship suddenly in early January. Lacrosse knew she was seeing another man, Deters said.

Sandstrom asked Deters if he watched the videotape of the police interview with Lacrosse the day of the killing in which Lacrosse told a number of lies. He said he watched it, but said Lacrosse was puzzled because he didn't know what happened during his dissociative state.

Black said the prosecution has to prove not only did Lacrosse commit the act charged, but that he had the requisite mental state. "One without the other is not enough," the lawyer said.